Hydrogen fluoride (HF) alkylation is an important refinery process in which isobutane is reacted with olefins to produce highly-branched isoparaffins as illustrated in FIG. 1 for use in gasoline blending. In this process, hydrofluoric (HF) acid functions as the catalyst and recirculates through the reactor. The recirculating HF acid catalyst is not pure; it contains a small amount of water and a reaction byproduct called acid-soluble oil. The catalyst is also saturated with the hydrocarbons involved in the process (e.g., alkylate and isobutane). In the HF alkylation process, it is important to monitor and control the purity of the catalyst since excessive amounts of water and acid-soluble-oil (ASO) have deleterious consequences: Excessive water, for example, can cause rapid corrosion of some carbon steel components.
Controlling the activity of the catalyst requires measuring the concentrations of HF acid, water, and ASO in a recirculating catalyst stream. Therefore, prior to this invention operators would take samples of the catalyst periodically and have these components measured by classical analytical techniques. There are several problems associated with this approach. First of all, HF acid will cause serious burns if it contacts skin. Because of this hazard, collecting and analyzing these samples carries potential for injury. Another problem is that the analytical methods used for these measurements lack precision, especially the method for ASO. This often makes it difficult to determine if the composition of the catalyst has truly changed from sample to sample. Finally, samples are drawn from the reactor only once or twice a day, and the analyses require several hours. This makes it difficult to follow the composition of the catalyst in a timely manner when processing changes do occur.
In the past few years, there has been a great deal of interest in on-line monitoring of various refinery process streams. In part, this interest has been spurred by advances in analytical technology that have greatly expanded the capabilities for process monitoring.
Accordingly, it is an object of the invention to continuously analyze hydrocarbon process streams containing acid catalyst, ASO and water.
It is a more specific object of this invention to improve precision and reduce the time required for analytical chemistry measurements of acid catalyst, ASO and water.
Yet another object is to reduce exposure of refining personnel to hazardous process chemicals.
Still another more specific object of this invention is to detect relatively small changes in ASO and other impurities in a recirculating catalyst stream that result in reduced catalyst activity.